There are many types of centrifugal pumps that are used in various industries to pump clear and solids-entrained fluids. Centrifugal pumps of the pitot tube type are typically used in industries where a high velocity output of the fluids being processed is desired. High velocity fluid output is achieved by pitot tube pumps as a result of their unique structure.
Centrifugal pumps of the pitot tube type generally include a rotating assembly made of at least two portions, which form, in combination, a fluid chamber therein. The rotating assembly turns within a chamber that is formed by an outer pump casing. An inlet delivers fluid into the fluid chamber of the rotating assembly via channels that are positioned generally at a perpendicular angle to the rotational axis of the rotating assembly. Consequently, the velocity of the fluid increases as it enters the rotating assembly. Fluid delivered to the rotating assembly is then forced to the outer periphery of the fluid chamber by centrifugal forces.
A pitot tube assembly that generally comprises at least one pickup tube, or blade, is stationarily positioned within the fluid chamber of the rotating assembly. A pitot tube arm, or extension arm, extends from the pickup tube in the same direction as the rotational axis of the rotating assembly. The extension arm is formed with a channel, which directs fluid to a discharge outlet of the pump.
The pickup tube of a pitot tube assembly is positioned within the fluid chamber of the rotating assembly. The pickup tube has an inlet that is positioned near the periphery of the inner wall of the fluid chamber. Fluid at the periphery of the rotating fluid chamber encounters the stationary inlet of the pickup tube and is forced into a channel formed in the pickup tube. The pickup tube channel or fluid pathway of the pickup tube is positioned generally perpendicular to the rotational axis. The fluid pathway of the pickup tube is in fluid communication with a channel in the pitot tube arm, which delivers the fluid to the discharge outlet of the pump at high velocity.
The nature of the fluid flow in a pitot tube pump produces increasing velocity of the fluid as it enters the pump inlet, is directed to the fluid chamber of the rotating assembly, and as it moves through the pickup tube to the discharge outlet. The increased fluid velocities in the rotating assembly can result in thrust balancing issues in the rotating assembly, which have been addressed in the prior art. Examples of pump structures that address thrust balance issues in the rotating assembly are described in U.S. Pat. No. 3,822,102 to Erickson, et al.; U.S. Pat. No. 4,183,713 to Erickson, et al., and U.S. Pat. No. 4,279,571 to Erickson.
Increasing velocity of the fluid entering into and moving through the pitot tube assembly also affect the stationary nature of the pitot tube assembly. That is, axial loads are experienced along the longitudinal axis of the pitot tube arm, or extension arm. Radial, tangential and axial loads are also experienced in the pitot tube assembly due to fluid pressures. The existence and deleterious effects of the forces that affect the pitot tube assembly, and attempts to overcome them, are discussed in U.S. Pat. No. 5,975,840, the contents of which are incorporated herein by reference. In the '840 patent, the axial loads and forces that adversely affect the structure and operation of the pitot tube assembly are addressed by the use of strategically placed locking nuts that place the extension arm in tension.
Locking nuts for this purpose have proven to be effective in addressing resistance to moments and forces experienced in the pitot tube assembly. However, the effectiveness of resistance is dependent upon the strength of the locking nuts, and the locking nuts or fastener clamping strength can fail due to overstress or fatigue. Additionally, the use of such fasteners often requires precise high-torque tensioning or the use of a hydraulic tensioning device to properly install the fastener. Improper installation can lead to failure or early wear.